Charleston, W.Va. -- After nearly three decades in the U.S. Senate, Democrat Jay Rockefeller of West Virginia said Friday he was ready to retire, calling his fight to protect the nation's coal miners one of his proudest achievements.

But in the waning days of his political career, the industry has grown hostile, with coal companies and their conservative allies accusing the five-term senator of being out of touch for defending clean-air regulations and other policies they say imperil the future of mining.

Rockefeller, the great-grandson of famed industrialist John D. Rockefeller, also was lambasted for supporting President Obama's health care overhaul as the president became ever more unpopular in West Virginia.

Rockefeller's retirement puts the seat held by Democrats since 1958 in jeopardy for the party, and well-liked Republican Rep. Shelley Moore Capito already has vowed to run in 2014.

The state is growing slightly more Republican: The GOP picked up 11 seats last fall in the state Legislature, and two of the three U.S. House seats are now held by Republicans.

At 75, Rockefeller said he wanted to focus on his family and called his decision entirely personal.

The peak of his career, he said, may have come in 1992, when he threatened to keep the Senate in session over Christmas break if they didn't pass legislation preserving retirement benefits for miners and their families. It passed, he said, and a nationwide strike was averted.

"I know the coal companies are going after me," Rockefeller said. "I can live with that, because I know that I am fighting every day for coal miners."

Rockefeller's positions in recent years have irritated some people trying to protect the 65,000 mining jobs in one of the country's poorest states.

In a speech on the Senate floor last summer, he chastised coal operators for using divisive scare tactics he said wrongly blame the federal government - and particularly the Obama administration - for the challenges they now face.

"The reality is that many who run the coal industry today would rather attack false enemies and deny real problems than find solutions," he said at the time.

Those challenges include not only clean-air regulations but also increasing competition from low-priced natural gas and an unchangeable geology that makes the remaining coal seams difficult and more expensive to mine.

Democrats, who hold a 55-45 edge in the Senate, will be defending 20 seats in next year's election while Republicans have 13 seats on the ballot.

New Jersey politics

Newark Mayor Cory Booker has taken an initial step toward running for U.S. Senate in 2014, adding intrigue to his political future and that of 88-year-old fellow Democrat Frank Lautenberg, who currently holds the seat.

Booker, perhaps New Jersey's highest-profile Democratic politician, filed paperwork with the Federal Election Commission on Tuesday that allows him to raise money for a Senate race. He did not make any public announcements about the filing.

His interest puts pressure on Lautenberg, the oldest member of the Senate. Lautenberg's spokesman, Caley Gray, said Friday that Lautenberg has not decided whether to seek re-election next year.

The Stanford-educated Booker has steadily built his national profile over the last six years as Newark's mayor.

Lautenberg has never given any indication that he would like to retire.